1. Field of the Invention
The invention relates to a process for the production of nonflammable molded parts, especially building material panels, in which vermiculite granules are expanded at an elevated temperature and then mixed with a binding agent, following which a bulk material or compressed cake is formed of the granulate, which has been coated with adhesive, and it is pressed into a nonflammable molded part.
2. Description of Related Art
In the production of nonflammable molded parts, it is known how to coat expanded materials such as vermiculite, perlite, or light expanded clay aggregate with binding agents comprised of inorganic and organic components, and then to compress them so that a connection of the expanded material particles to each other arises. Due to the fact that condensation resins, such as formaldehyde condensation resins, for example, are used as organic components, it has been shown that, due to the processing parameters during the compression procedure, compounds of these resins that have a low molecular weight, such as formaldehyde, are liberated. As a result, these well-known methods have proven to be a relatively large source of environmental pollution.
Now it is the task of the invention to indicate a process of the type mentioned at the outset for the production of nonflammable molded parts that is environmentally friendly and yields satisfactory properties at the end product of the process, such as its mechanical stability and absence of flammability.
According to the invention, therefore, a process of the type mentioned at the outset is proposed, which is characterized by the fact that the expanded vermiculite granulate is furnished with an application of an adhesive coating comprised of a solution of an inorganic binding agent, and that the coated vermiculite granulate is precompressed, continuously or discontinuously, cut to the shape of the individual piece, and that these custom-cut pieces are compressed discontinuously at room temperature or higher, preferably at temperatures of at least 100xc2x0 C., and at pressures of at least 0.3 N/mm2, so that all solvent residues are removed from the final, finished, nonflammable molded part.
An advantage of the process according to the invention resides in the fact that the discontinuous hot compression occurs in a press that is heated by the usual heating media, and by means of high-frequency current as well. Furthermore, the discontinuous hot compression occurs, to good advantage, in the presence of a steam sieve for the purpose of removing solvent residues. Similarly, in the case of the continuous precompression, cover sheets arranged on one or both sides of the bulk cake can be compressed with the cake to good effect.
In the process according to the invention, a binding agent that contains phosphorus is used to good advantage as an inorganic binding agent, such that those that are based upon acids that contain phosphorus, and/or their salts, are particularly well-suited.
Furthermore, silicate compounds can be used to good effect as inorganic binding agents, preferably silicate of potassium or sodium, hydraulic binders, preferably cement, Sorel binders, as well as hemihydratic or hydratic binders, such as gypsum. Other additives, preferably agents that render the solution hydrophobic, may be added to the solution of inorganic binding agents as well.